1. Field the Invention
This invention relates to a switching circuit apparatus, and more particularly to a switching circuit apparatus which may be adapted to a modulator, demodulator and the like.
2. Description of the Prior Art
Switching circuit apparatus adapted for modulators or demodulators are conventionally constructed by using a pair of switching circuits connected in parallel with each other to a DC power source. Each switching circuit is connected for receiving an input electrical signal to be switched, i.e., a switched signal, and another electrical signal with a given frequency for switching, i.e., a switching signal. The switching signal is applied to respective switching circuits in antiphase for alternately setting the switching circuits in an operative or inoperative condition so that the switched signal applied to respective switching circuits in the same phase is divided between output circuits of the switching circuits alternately in synchronism to the given frequency of the switching signal.
Thus switching circuit apparatus used for modulators modulates the switched signal with the switching signal of a given frequency. On the other hand, switching circuit apparatus used for demodulators demodulates a resultant signal modulated in the switched signal by a given frequency of the switching signal from the switched signal.
In prior art switching circuit apparatus, the pair of switching circuits are supplied a switching signal having square waveform at a 50% duty ratio. Although ideally the waveforms are square waves, they are in practice rounded at their transition edge portions due to influences of signal delay and stray capacitance in the transistor circuits. The pair of switching circuits connected in parallel with each other to the power supply source are both simultaneously put in operative conditions at transition edge portions of the waveforms, i.e., switching transition period of the switching circuit apparatus. The prior art switching circuit apparatus have drawbacks because the switched signal leaks to an undesired one of the switching circuits. Consequently, the prior art switching circuit apparatus fail to divide the switched signal into respective output circuits of the pair of switching circuits. Further, biasing currents from the power source flow through the switching circuits simultaneously at the switching transition period so that power source voltage is sufficiently lowered that the switching circuits will not operate properly. Thus prior art switching circuit apparatus require power sources supplying relatively high voltage.
An example of a prior art switching circuit apparatus is shown in FIG. 1 and is more fully discussed using FIG. 2 below in the Description of the Preferred Embodiment.